A conventional stringed instrument such as a guitar usually has a tuning machine to adjust the tension of strings (referring to FIG. 1). Refer to FIGS. 2, 3 and 4 for a conventional tuning machine of a guitar. It includes a hollow dock 1 which is extended longitudinally from the bottom to form a duct to couple with a winding axle 2. The winding axle 2 has an upper end coupled with a worm gear 3 held in the dock 1 and a lower side with a string hole formed thereon to be threaded through by a string for fastening. The dock 1 also has a transverse sleeve 4 to be run through a worm 5 to engage with the worm gear 3 to drive and turn the worm gear 3. The worm 5 has one end formed a coupling portion 5a which has two opposing planes. A rotary knob 6 is provided that has a through hole in the center that also has two opposing planes to couple with the coupling portion 5a of the worm 5. The rotary knob 6 is fastened to the worm 5 through a screw 5b from an outer side of the rotary knob 6 into a screw hole formed in the coupling portion 5a. The winding axle 2 has another screw hole 2a in the center of an upper end thereof to be fastened by another screw 7 to anchor the winding axle 2. The dock 1 has an opening 8 at the top to be sealed by a lid 9.
By turning the winding axle 6 the worm 5 can be rotated in a positive direction or a negative direction to drive the worm gear 3 to rotate in the positive or negative direction, and the string can be wound tighter or loosened as desired.
The conventional guitar tuning machine set forth above consists of a great number of elements. The worm 5 and rotary knob 6 have to be fabricated separately, then to be fastened through the screw 5b. The worm 5 and the through hole of the rotary knob 6 have to form two planes to make coupling and turning possible. Moreover, two washers have to be provided between the rotary knob 6 and the dock 1. All this increases fabrication process and production cost. The winding axle 2 further has to be fastened by another screw 7 to couple with the dock 1. As a result the cost and price are higher. And product competitiveness on the market suffers.